The demand for coniferous trees, such as pines and firs, to make wood products continues to increase. One proposed solution to the problem of providing an adequate supply of coniferous trees is to identify individual coniferous trees that possess desirable characteristics, such as a rapid rate of growth, and to produce numerous, genetically identical, clones of the superior trees by somatic cloning.
Somatic cloning is the process of creating genetically identical trees from tree somatic tissue. Tree somatic tissue is tree tissue other than the male and female gametes. In one approach to somatic cloning, tree somatic tissue is cultured in an initiation medium which includes hormones, such as auxins and/or cytokinins, that initiate formation of embryogenic cells that are capable of developing into somatic embryos. The embryogenic cells are then further cultured in a maintenance medium that promotes multiplication of the embryogenic cells to form pre-cotyledonary embryos (i.e., embryos that do not possess cotyledons). The multiplied embryogenic cells are then cultured in a development medium that promotes development and maturation of cotyledonary somatic embryos which can, for example, be placed within artificial seeds and sown in the soil where they germinate to yield conifer seedlings. The seedlings can be transplanted to a growth site for subsequent growth and eventual harvesting to yield lumber, or wood-derived products. Alternatively, the cotyledonary somatic embryos can also be germinated in a germination medium, and thereafter transferred to soil for further growth.
A continuing problem with somatic cloning of conifer embryos is stimulating efficient and cost-effective formation of somatic embryos that are capable of germinating to yield plants. Preferably, conifer somatic embryos, formed in vitro, are physically and physiologically similar, or identical, to conifer zygotic embryos formed in vivo in conifer seeds. There is, therefore, a continuing need for methods for producing viable conifer somatic embryos from conifer embryogenic cells.